摘要
多基站协作预编码技术,充分利用用户有限的信道状态信息,在发送端对传输数据进行协作预编码,使系统在误码率性能、频谱效率和降低复杂度上得到了很大的改善,成为当前无线通信领域研究的热点之一。本文以消除蜂窝MIMO系统同频干扰和优化吞吐率性能为目标,对协作预编码技术进行了深入的理论研究与仿真分析,主要研究内容如下：
(1)基于蜂窝多小区拓补结构,研究了传统的线性预编码技术和基于信道反馈的波束赋形预编码方案,并对线性预编码设计的迭代注水功率分配方法进行了研究,提出了改进的波束赋形方案,通过仿真验证了该方案在不同的用户数规模下,均能够达到较好的干扰抑制能力和更为稳健的吞吐率性能；
(2)研究了多基站协作预编码技术,对部分协作条件下的干扰迫零技术进行了改进,通过选取不同的等效空间子信道,使邻小区同频干扰的抑制和系统吞吐率性能的提高,可以依据实际用户的服务质量要求进行折中取优；提出了基于用户上行干扰信道反馈的多基站协作块对角化方案,通过仿真验证了该方法在消除用户同频干扰信号上的优越性,且能够达到渐进最优的系统吞吐率性能,并与改进迫零方案进行了性能的比较；
(3)研究了基于最大化信号泄漏噪声比的协作波束赋形策略,并且通过数据仿真验证了该方案,在任意发送信噪比条件下,通过平衡波束之间的功率分配,大大提高了系统的吞吐量,且在很宽的信噪比范围内与理想DPC方案非常接近；同时,提出了基于PMI反馈的折中策略,通过仿真展示了该折中策略在抑制边缘用户的邻小区干扰以及提高系统吞吐率性能上的优越性；
(4)提出了一种基于最优化协作基站组的折中协作策略,通过最大化系统吞吐率来选择最佳的协作小区基站,同时对边缘用户的调度问题进行详细的研究,提出了基于信干噪比判决门限的边缘用户调度方法,并与传统的用户调度方式以及正比公平调度进行了比较,在此基础上通过SVD方法设计预编码,通过数据仿真,验证了该策略有效提高了系统容量的断线性能,并且以较低的算法复杂度在系统的频谱效率的提高和边缘用户的公平性之间有一个很好的折中,具有很好的实用价值。
With limited channel state information (CSI) of the mobile stations (MS), base stations (BS) cooperate to preprocess the transmission, improving the bit error rate (BER) performance, spectral efficiency, and becoming one of the research focuses in the field of wireless communications. Revolving around removing the co-channel interference (CCI) and optimizing the throughput, this paper investigates the cooperation pre-coding schemes in depth and does related simulation analysis. The main contents are as follows:
(1) The main statistical properties of the MIMO channel are outlined based on the multi-cell cellular structure. For multi-user MIMO systems, different scheduling algorithms are investigated and analyzed on supporting the system throughput and ensuring the edge users' fairness via simulations.
(2) Linear pre-coding are investigated. Zero-forcing (ZF) and beam-forming schemes are introduced. For the power allocation of linear pre-coding, due to the iterative water filling (IWF), the optimal throughput is capable and the simulation shows the superiority of the algorithm. On this basis, the improved beamforming strategy based on CSI feedback is proposed, which is verified feasibly via the simulation on removing the CCI and improving the throughput.
(3) Based on the multi-cell transmission, an improved interference ZF technique is proposed for a compromise between the throughput and interference removing. A collaborative block diagonalization scheme via CSI feedback is proposed and verified superior by simulation on removing the CCI and improving the throughput. Based on the beamforming, collaborative beamforming scheme with maximizing the signal to leakage plus noise ratio (SLNR) is investigated and verified feasible. A strategy based on the optimization of collaborative BS group is proposed, which is verified capable on improving the throughput break performance. Through simulations the proposed strategy is proved a good compromise between spectral efficiency, the algorithm complexity and the user's fairness with good practical value. The compromised strategy based on the PMI feedback is studied and the simulation shows it to inhibit the edge users'adjacent-cell interference and increase the throughput performance. Finally, a number of issues about the cooperation pre-coding techniques are prospected.
引文
[1]S. Catreux, P. F. Driessen, and L. J. Greenstein. Simulation results for an interference-limited multiple- input multiple-output cellular system. IEEE Communications Letters,2000,4:334～336.
[2]Z.Ping, T.Xiaofeng, Z,Jianhua, W.Ying, L.Lihua, and W.Yong. A vision from the future: beyond 3G TDD. Communications Magazine,IEEE,2005,43:38～44.
[3]X, Tao, L. Ni, Z.Dai,1. Liu Bao, and P. Zhang. Intelligent group handover mode in multicell infrastructure. In Personal, Indoor and Mobile Radio Communications,2003. PIMRC2003.14th IEEE Proceedings on,2003.351!354.
[4]S. A. Jafar, G. J. Foschini, and A. J. Goldsmith. PhantomNet:exploring optimal multicellular multiple antenna systems. In Vehicular Technology Conference,2002. Proceedings. VTC 2002-Fall.2002 IEEE 56th,2002,261～265.
[5]H. Huang and V. Sivarama. Asymptotic downlink capacity of coordinated cellular networks. In Signals, Systems and Computers,2004. Conference Record of the Thirty-Eighth Asilomar Conference on,2004,850～855.
[6]N. Boon Loong, J. S. Evans, S. V. Hanly, and D. Aktas. Transmit beamforming with cooperative base stations. In Information Theory,2005. Proceedings. International Symposium on,2005,1431～1435.
[7]G. J. Foschini, K. Karakayali, and R. A. Valenzuela. Coordinating multiple antenna cellular networks to achieve enormous spectral efficiency. Communications, IEE Proceedings,2006, 153:548～555.
[8]M. K. Karakayali, G. J. Foschini, R. A. Valenzuela, and R. D. Yates. On the Maximum Common Rate Achievable in a Coordinated Network. In Communications,2006. ICC'06. IEEE International Conference on,2006,4333～4338.
[9]H. Zhang and H. Dai, in 2004 Conference on Information Sciences and Systems Princeton University,2004.
[10]O. Somekh, O. Simeone, Y. Bar-Ness, and A. M. Haimovich. CTH11-2:Distributed Multi-Cell Zero-Forcing Beamforming in Cellular Downlink Channels. In Global Telecommunications Conference,2006. GLOBECOM'06. IEEE,2006.1～6.
[11]Luca Venturino, Narayan Prasad, Xiaodong Wang. Coordinated Linear Beamforming in Downlink Multi-Cell Wireless Networks. IEEE Transactions On Wireless Communications, 2010,9(4):1451～1461.
[12]Hayssam Dahrouj, Wei Yu. Coordinated Beamforming for the Multi-Antenna Wireless System. IEEE Transactions On Wireless Communications, May 2010,9:1748～1759.
[13]Emil Bjornson, Randa Zakhour, David Gesbert, Bjorn Ottersten. Cooperative Multicell Preceding:Rate ReginCharacterization and Distributed Strategies WithInstantaneous and Statical CSI. IEEE Trasactions On Signal Processing, Aug 2010,58:4298～4310.
[14]F. Boccardi and H. Huang, "Zero-forcing precoding for the MIMO broadcast channel under per-antenna power constraints," in Proc. IEEE PAWC, Cannes, July 2006, pp.1-5.
[15]S. Shim, J. S. Kwak, R. W. H. Jr., and J. G. Andrews, "Block diagonalization for multi-user mimo with other-cell interference," IEEE Transactions on Wireless Communications, vol.7, pp.2671-2681, July 2008.
[16]Jun Zhang, Runhua Chen, Jeffrey G. Andrews, Arunabha Ghosh, and Robert W. Heath, Jr., "Networked MIMO with Clustered Linear Precoding",IEEE Transactions on wireless communications, Vol.8, No.4, April 2009.
[17]E. Bjormson, R. Zakhour, D. Gesbert, B. Ottersten. Distributed multicell and multiantenna precoding:characterization and performance evaluation. In Proc. Of IEEE Globecom Conference, Hawai,2009.
[18]H. Weingarten, Y. Steinberg, and S. Shamai (Shittz). The capacity region of the Gaussian Multiple-Input Multiple-Output broadcast channel. IEEE Trans. Inform. Theory,2006, 52(9):3936～3964.
[19]S. A. Jafar and A. Goldsmith. On optimality of beamforming for multiple antenna systems with imperfect feedback. In Proc. ISIT 2001-IEEE Int. Symp. Information Theory, Washington, DC, June 2001.
[20]S. Shamai (Shitz), O. Somekh, and B. M. Zaidel. Multi-cell communications:An information theoretic perspective. In Joint Workshop on Communications and Coding (JWCC), Florence, Italy, Oct 2004.
[21]O. Somekh, B. M. Zaidel, and S. Shamai (Shitz). Sum rate characterization of joint multiple cell-site processing. IEEE Trans. Inform. Theory, Dec 2007,53:4473～4497.
[22]MIMO Wireless Communications. Cambridge University Press,2006.
[23]M. K. Simon. Evaluation of average bit error probability for space-time coding based on a simpler exact evaluation of pairwise error probability. Journal of Communications and Networks,3(3):257-264, September 2001.
[24]D. Bertsekas and R. Gallagar. Data Networks:Prentice-Hall.1992.
[25]C. Wengerter, J. Ohlhorst, and A. G. E. v. Elbwart. Fairness and Throughput Analsis for Generalized Proportional Fair Frequency Scheduling in OFDMA. VTC'05 Spring,2005. 1903～1907.
[26]W. Yu, W. Rhee, S. Boyd, and J. Cioffi. Iterative water-filling for Gaussian vector multiple-access channel. IEEE Trans. Inf. Theory,2004,50(5):145～152.
[27]E. Telatar. Capacity of multi-antenna Gaussian channels. Europ. Trans. Telecommun., ETT, 1999,10(6):585～596.
[28]N. Jinda, W. Rhee, S. Vishwanath, S. A. Jafar and A. Goldsmith. Sum Power Interative Water-Filling for Multi-Antenna Gaussian Broadcast Channels. IEEE Trans. Information Theory, Apr 2005,51(4):1570～1580.
[29]M. Sharif and B. Hassibi,2007. Scaling Laws of Sum Rate Using Time-sharing, DPC and Beamforming for MIMO Broadcast Channels. IEEE Transaction on Communications,55(1): 11～15.
[30]D. J. Love and R. W. Heath. Limited feedback unitary precoding for orthogonal space-time block codes. IEEE Trans. Signal Processing,53(1):64～73, January 2005.
[31]S. Shamai (Shitz) and B. M. Zaidel. Enhancing the cellular downlink capacity via co-processing at the transmitting end. In Proc. IEEE Veh. Technol. Conf., Rhodes, Greece, pp. May 2001.1745～1749.
[32]S. A. Jafar, G. Foschini, and A. J. Goldsmith. Phantomnet:Exploring optimal multicellular multiple antenna systems. EURASIP Journal on Appl. Signal Processing, Special issue on MIMO Comm. and Signal Processing, May 2004.591～605.
[33]A. Goldsmith, S. A. Jafar, N. Jindal, and S. Vishwanath. Capacity limits of MIMO channels. Selected Areas in Communications, IEEE Journal on, vol.21,2003.684～702.
[34]G. J. Foschini, K. Karakayali, and R. A. Valenzuela. Coordinating multiple antenna cellular networks to achieve enormous spectral efficiency. Communications, IEE Proceedings-, vol. 153,2006.548～555.
[35]P. W. Baier, M. Meurer, T. Weber, and H. Troger. Joint transmission(JT), an alternative rationale for the downlink of time division CDMA using multi-element transmit antennas. In Spread Spectrum Techniques and Applications,2000 IEEE Sixth International Symposium on, vol.1,2000.1～5.
[36]S. Shamai and B. M. Zaidel. Enhancing the cellular downlink capacity via co-processing at the transmitting end. In Vehicular Technology Conference,2001. VTC 2001 Spring. IEEE VTS 53rd, vol.3,2001.1745～1749.
[37]Q. H. Spencer, A. L. Swindlehurst, and M. Haardt. Zero-forcing methods for downlink spatial multiplexing in multiuser MIMO channels. Signal Processing, IEEE Transactions on [see also Acoustics, Speech, and Signal Processing, IEEE Transactions on], vol.52,2004. 461～471.
[38]G.H. Golub and C.F.V. Loan, Matrix Computations, The Johns Hopkins University Press,3 edition,1996.
[39]C. Windpassinger, R. F. H. Fischer, T. Vencel, and J. B. Huber, "Precoding in multiantenna and multiuser communications," IEEE Trans. Wireless Commun., vol.3, pp.1305-1316, July 2004.
[40]H. Zhang and H. Dai, "Cochannel interference mitigation and cooperative processing in downlink multicell multiuser MIMO networks," European J. Wireless Commun. Networking, pp.222-235,2004.
[41]A. Tarighat, M. Sadek, and A. H. Sayed, "A multiuser beamforming scheme for downlink MIMO channels based on maximizing signal-toleakage ratios," in Proc. ICASSP,2005, pp. 1129-1132.
[42]L. Venturino, N. Prasad, and X. Wang. An improved iterative water-filling algorithm for multi-cell interference mitigation in downlink OFDMA networks. In Proc. Asilomar Conf. Signals, Syst., Comput., Pacific Grove, CA, Nov 2007.
[43]Coordinated scheduling and power allocation in downlink multi-cell OFDMA networks. IEEE Trans. Veh. Technol.,2009,58(6):2835～2848.
[44]W. Yu. Multi-user water-filling in the presence of crosstalk. In Proc.2007 Inf. Yheory Appl. Workshop, San Diego, CA, Jan 2007.
[45]R. A. Horn and C. R. Johnson, Matrix Analysis. Cambridge, UK:Cambridge University Press,1996.
[46]H. Zhang and H. Dai, "Co-channel interference mitigation and cooperative processing in downlink multicell multiuser MIMO networks," European J. Wireless Commun. and Networking, no.2, pp.222-235,4th Quarter 2004.
[47]G. Caire, S. A. Ramprashad, H. C. Papadoupoulos, C. Pepin, and C.-E. W. Sundberg, "Multiuser MIMO downlink with limited inter-cell cooperation:approximate interference alignment in time, frequency, and space," in Proc. Allerton Conf. on Comm. Control and Comp., Monticello, IL, Sept.2008.
[48]A. Tarighat, M. Sadek, and A. H. Sayed. A multi user beamforming scheme for downlink MIMO channels based on maximizing signal to leakage ratios. In Proc.2005 IEEE International Conf. Acoustics, Speech, Signal Process., vol.3, Philadelphia, PA, Mar 2005. 1129-1132.
[49]PMI restriction for the downlink closed-loop MIMO, IEEE Std. IEEEC802.16m-08/430, 2008.
[50]L. Falconetti and C. Hoymann "Codebook based Inter-Cell Interference Coordination for LTE," IEEE Personal Indoor and Mobile Radio communications (PIMRC), Sep.2010.
[51]J. H. Conway, R. H. Hardin and N. J. A. Sloane, "Packing Lines, Planes, etc.:Packing in Grassmannian Spaces," Experimental Mathematics, vol.5, pp.139-159,1996.
[52]Arogyaswami Paulraj, Rohit Nabar, Dhananjay Gore著,刘威鑫译,空时无线通信导论,清华大学出版社,2007.
[53]Claude Oestges, Bruno Clerckx著,赵晓晖译,MIMO无线通信,机械工业出版社,2010.
[54]康桂华著,MIMO无线通信原理及应用,电子工业出版社,2009.
[55]David Tse, Pramod Viswanath著,李锵,周进等译,无线通信基础,人民邮电出版社,2007.
[56]周恩,张兴,吕召彪,孙宇吴编著,下一代宽带无线通信OFDM与MIMO技术,人民邮电出版社,2008.